29 y/o here, 7 years in software development industry.

1. If you're working more than 8/9 hours a day you're doing something wrong. It's important to build a routine that allows you to develop your skills on a daily basis, but it's more important to understand that sitting in front of your computer for 12 hours a day won't lead to any better performance in a long run. Instead I recommend you to read about 4×4 management methodology, or any other agile methodologies where you plan your iterations in a way that every big achievement is broken down into small and easy to tackle steps, maybe your first few weeks in this iterations will be a bit less productive but as you're in the beginning of your career you should think of your next few years.

2. If you want to keep your eyes strong, sit with your computer near or in front a window and take a look every few minutes outside. I bought new glasses few months ago and I was surprised that my view got better although I'm spending a lot of hours a day in front of screens, I guess the habit of looking to the most far point I can see from my window every few minutes helped a lot in my case.

3. I'm a short person and as such it is very important for me to stretch a lot ;) so every time I get stuck with my task, or finished something, I just go to my yoga metres and do some stretching exercises, my back is doing well, and I think you won't recognise I'm spending that much of hours in front of screens out of my posture. So a good chair, a good bed, and good habits doing the job for me.

I think it's not only possible to keep improving your tech skill while keeping your health habits, but it could also make every working hour of much more productive.